Microlithographic projection exposure apparatuses are used for producing microstructured components, such as integrated circuits or LCDs, for example. Such a projection exposure apparatus has an illumination device and a projection lens. In the microlithographic process, the image of a mask (=reticle) illuminated with the aid of the illumination device is projected via the projection lens onto a substrate (e.g. a silicon wafer) coated with a light-sensitive layer (photoresist) and arranged in the image plane of the projection lens, in order to transfer the mask structure to the light-sensitive coating of the substrate.
During the operation of a microlithographic projection exposure apparatus, it is desirable to set defined illumination settings, i.e. intensity distributions in a pupil plane of the illumination device, in a targeted manner. For this purpose, in addition to the use of diffractive optical elements (so-called DOEs), the use of mirror arrangements is also known, e.g. from WO 2005/026843 A2. Such mirror arrangements include a multiplicity of micromirrors that can be set independently of one another, and enable the flexible variation of the intensity distribution set in the illumination device.
In this case, in practice the maximum settable tilting angles of the mirror elements within such a mirror arrangement for setting the respectively desired illumination settings are limited (typically to a few degrees), in order to avoid mechanical problems when realizing the tilting of the mirror elements (e.g. owing to an instability of the flexures typically used there) and, if appropriate, problems appertaining to the dissipation of heat in the region of the mirror arrangement. This restriction of the maximum tilting angles within the mirror arrangement in turn has the effect that a Fourier optical unit that is typically used in the illumination device and serves for converting the angular distribution of the illumination light into a spatial distribution in the pupil plane typically has to have relatively long focal lengths (e.g. several meters).
In order to realize these focal lengths with a still tenable outlay, it is known to configure the Fourier optical unit as an optical zoom system with a plurality of refractive lens elements, but in principle this increases the outlay in respect of material and costs. Furthermore, the configuration of the Fourier optical unit as an optical zoom system with a plurality of refractive lens elements can also mean an increased structural outlay in the configuration of the optical design of the projection exposure apparatus insofar as e.g. the accommodation of supporting structures, which is likewise involved spatially and which desirably is not be impeded by the additional lens elements within the optical zoom system, is made more difficult.
With regard to the prior art, reference is made, merely by way of example, to WO 2005/026843 A2, US 2009/0116093 A1 and US 2006/055834 A1.